Directional antenna



w. s. EATON 2,204,405 DIRECTIONAL ANTENNA Filed Jan. 50, 1959 J: #50 0? mam 44s Patented June 11, 1940 UNITED STATES PATENT QFFEQE DIRECTIONAL ANTENNA of Delaware Application January 30, 1939, Serial no. 253,709

11 Claims.

This invention relates to a directional antenna and in particular to a directional antenna which may be used for indicating radio bearings substantially free from night effect. Numerous articles have been written about night effect. This term is used to describe the variations of intensity and apparent direction of radio waves in their propagation during the period from approximately sundown to sunrise. During these hours an ionized region or layer above the earths surface becomes a reflector of radio waves. The reflected wave energy may reach a receiver at an entirely difierent phase from the directly transmitted ground wave. Furthermore, it has been shown that the reflected wave energy may be abnormally polarized.

One of the results of night effect is to cause variations of the received signal; another effect is to cause an apparent change of bearing as indicated by radio direction finders. Such apparent changes in bearing may amount to as much as or more degrees during an interval of several minutes. Since the average loop antenna is particularly responsive to sky waves, it follows that the loop is a poor instrumentality for indicating radio bearings during the existence of night effects.

Adcock and Ellis in their British Patent 130,490 have proposed a system of antennas for indicating radio bearings. This system is very much less responsive to sky waves and therefore produces an improved indication. However, the socalled Adcock antennas are not well suited to installation on aircraft and other small vehicles where space is at a premium.

The present invention has for one of its objects the provision of means for reducing night effects. Another object is to provide a directional antenna system for indicating radio bearings. A still further object is to provide an antenna substantially free from night efiects and arranged to occupy a relatively small space.

The invention will be described by reference to the accompanying drawing in which Figure l is a schematic circuit diagram representing one embodiment of the invention; Figure 2 is a sectional view of one of the elements of the invention; and Figure 3 is a response pattern of the directive antenna.

Referring to Fig. 1, a plurality of turns of conductive wire I are arranged in a D-shape. Each portion of all of the turns, excepting the vertical portion, is arranged within a shield 3. The terminals are connected to a variable tuning capacitor 5. A unilateral connection 1 is made from the tuning capacitor through a capacitor 9 to the control electrode ll of a thermionic tube 13. The control electrode H is connected to ground through a resistor I5. The output of the thermionic tube is coupled to the balance of a conventional radio receiver which may be of the tuned radio frequency amplifier, superheterodyne or like circuit. The output of the radio receiver is applied to an indicator l1. It will be observed that the shield 3 is grounded. A vertical antenna I9 is connected to the unilateral connection I.

By way of example, I have constructed the shielded antenna. so that the exposed vertical portion is about nine inches long and consists of 26 15 turns of No. 22 insulated copper wire. The curved portion of the turns is arranged on a form Whose radius is approximately 5". The shield may be constructed from any suitable conductor. The several turns of conductor may extend over more than one layer, as indicated in Fig. 2. It will be observed that the input circuit to the radio receiver does not correspond to a conventional input circuit. The variable capacitor 5, which is used to resonate the inductor l, is connected in a novel manner which permits electrostatic and electromagnetic shielding of all portions of the turns and circuits except the vertical portion. The shielding is made complete with the exception of small apertures which just admit so the conductors.

Since the inductor may be resonated at the operating frequency, and since the shield is effectively coupled to the inductor by inherent capacities, represented by the dash lines 2!), it folllows that the shield itself may participate of the resonant characteristics of the inductor. Although the theory of operation is not well understood and without being limited to any particu lar mode of operation, it is believed that the shield operates as a parasitic reflector with re spect to the vertical portions of the inductor. In this manner, the vertical portions of the inductor are one element of the directive antenna While the shield becomes another element. Radio waves, intercepted by the antenna elements, induce electromotive forces which are not of the same phase when the two elements lie along the direction of wave propagation. When the elements are parallel to the wave front, the induced electromotive forces are of similar phase. Thus the resultant characteristic may be represented as a figure 8 response when plotted in terms of polar coordinates. This is indicated by the curve 2| of Figure 3. The antenna l9 has a non-direc- 55 duce substantially no electromotive forces and therefore the device is substantially free from night effect. In an. actual demonstration it has been shown that a loop radio direction finder gave erratic bearing indications with respect to transmitters located at distances varying from 125 to 400 miles. During the interval when erratic bearing indications were obtained by means I of the loop, reliable bearings were indicated by the direction antenna of the invention. In practice it is preferable to rotate the loop at avelocity of the order of 10 revolutions per second about an axis indicated by the broken line ill. The phase of currents induced inv the directive antenna is compared to a reference phase to indicate bearings in terms of 360 degrees.

Thus the invention has been described as a directional antenna which is substantially free from night effects. antenna is shielded with the exception of the vertical portion. Shielding acts as a parasitic antenna. the input of a radio receiver or other load circuit in a novel manner whereby potentials established in the shield, in the vertical portions of the inductor and in a non-directive antenna, may be applied to the receiver. It should be understood that the shielded inductor described above has been offered by way of illustration rather than limitation. The dimensions should be chosen with reference to the operating frequency and conditions. Furthermore, the antenna system may be rotated manually rather than by a continuously operated motor. Likewise, the .indi cator may be responsive over 360 or less. The non-directive antenna may be omitted.

While the invention has been described as useful in eliminating the reception of sky waves, it should be understood that the system may be used to eliminate ground waves and receive the sky wave.

I claim as my invention:

1. A directional antenna including an inductor, means for shielding said inductor, said inductor including an unshielded portion equal to a substantial fraction of the total inductor and responsive to radio waves whose direction is to be indicated, means for tuning said inductor, means for connecting said shield to a load circuit, and a unilateral connection from said inductor to said load circuit.

2. A directional antenna including a shield, an inductor having substantially two-thirds enclosed within said shield and having the unshielded portion responsive to radio waves whose direction is to be determined, means for resonating The inductor portion of the The directive antenna is connected to said inductor, input circuit connections, a connection' from said input circuit to said shield, and a unilateral connection from said input circuit connections to said-inductor.

3. A directional antenna including an electric and magnetic shield, an inductor having substantially one-third exposed and substantially two-thirds enclosed within said shield, a pair of terminals for said antenna, a unilateral connection from one of said termials to said inductor, and a connection from said shield to the other of said terminals.

4. In a directional antenna system, a D-shape inductor, means for shielding only the curve portion of said D-shape inductor, a pair of terminals, a unilateral connection from said inductor to one of said terminals, said unilateral connection being the sole connection from said inductor to said terminals, and a connection from the other of said terminals to said shield.

5. In a system of the character of claim 4, means for tuning said inductor.

6. In a directional antenna, an inductor including a vertical portion, means for tuning said inductor, means for completely shielding all but the vertical section of said inductor, a pair of terminal connections for said antenna, a connection from one of said terminals to said tuning means, said last mentioned connection being thesole connection from said inductorto said terminals, and a connection from said shielding means to the other of said terminals.

7. In an antenna of the character of claim 1, a sense antenna effectively connected to said unilateral connection.

8. In a system of the character of claim 4, a sense antenna effectively connected to said unilateral connection.

9. In a directional antenna an inductor, an enclosure shielding all but an exposed portion of said inductor, said enclosure being eifectively coupled to said inductor, said exposed portion being responsive to radio waves whose fronts are to be determined, means for tuning said inductor, said coupling imparting said tuning to said enclosure, and means for utilizing the exposed por tion of the inductor and the enclosure as the ele ments of said directional antenna.

10. In a device of the character described, an inductor, a conductive shield covering all but approximately a third of said inductor, a capacitor for resonating said inductor, said shield being efiectively coupled to said inductor so that the resonated characteristics of said inductor are imparted to said shield, and means for connecting the third of said inductor and the shield to a load circuit whereby said third of said inductor and said shield become the elements of a directive antenna.

11. In an antenna system, an inductor, a shield enclosing substantially two-thirds of said inductor, means for'tuning said inductor and said shield, and means for utilizing the unenc-losed part of said inductor and said shield as the elements of the antenna system.

WARREN s. EATON. 

